The present invention relates generally to piezoelectric sensors of the type employed for sensing a transient or momentary mechanical displacement, deformation or strain and generating a corresponding output signal. More particularly, the present invention relates to piezoelectric sensors having notable utility in connection with an internal combustion engine fuel injection system for generating a reference fuel injection timing signal.
A number of devices and methods have been advanced for sensing a pressure pulse in a conduit, such as a fuel line, by means of a piezoelectric transducer. For example, Beatson et al U.S. Pat. No. 4,146,875 discloses a pressure sensing device wherein an electrical transducer is mounted upon a flexing portion of a ring which surrounds a body subjected to internal pressure. One application of the device clamps around an engine fuel line to sense fuel pressure. In Beatson et al U.S. Pat. No. 4,257,260, an engine analyzing apparatus senses pressure in fuel lines by means of piezoelectric crystals symmetrically located at opposing positions of a fuel line. The transducers generate electric signals in response to a bending stress caused by periodic dilation of the pipe resulting from pressure pulses within the pipe. Beatson et al British Patent No. 1,389,408 discloses a pair of pressure sensing elements such as transducers which convert a mechanical load pressure within a fuel line pipe to an electrical signal.
Wessel U.S. Pat. No. 4,430,899 discloses a fluid pressure sensor employed in conjunction with a diesel engine injection pump wherein a strain bolt is tapped into a bore extending through a housing wall. The bolt has a bore which extends therethrough and a region of reduced outer diameter which forms a thin wall tubular sleeve-like region. Two oppositely polarized piezoelectric transducer discs are clamped between the outer wall of the housing so that upon application of a fluid pressure and resultant straining of the thin wall portion of the bolt, an output signal is generated.
Claassen et al U.S. Pat. No. 4,194,401 discloses a transducer for measuring the internal pressure in injection pipes of diesel engines. A rigid housing encloses the injection pipe and at least one elastic sensor is arranged inside the housing adjacent to a portion of the circumference of the pipe. An endorsing element elastically forces the sensor element against the pipe whereby deformations of the pipe are transmitted frictionally to the sensor element for generating an electrical signal indicative of the pressure induced strain on the pipe.
Russell U.S. Pat. No. 3,898,885 discloses a fluid pressure transducer wherein transducer sensing numbers are mounted on arms which ae pivotally mounted to permit engagement of the sensing members with a pipe. The arms have frictional engagement with a pair of plates to provide damping of the movement of the members due to variations of the diameter of the pipe.
Yelke U.S. Pat. No. 4,304,126 also discloses a transducer for sensing and monitoring the injection of fuel into a fuel injection type engine. The transducer comprises a flexible collar and a flexible piezoelectric element mounted on the fuel line to sense the change in the circumferential dimension of the line due to the pressure pulse created as fuel is injected through the line into the engine.